1. Field of the Invention
This invention relates to a method for inspection of an electronic state of a surface of a semiconductor substrate and an apparatus therefor, and more particularly relates to a technique of inspecting an electronic state of a surface of the substrate by generating electron hole pairs thereon and measuring absorption of electromagnetic wave thereof. The term "electronic state" as used herein and in the appended claims means the recombination rate of excess carriers or the concentration of recombination centers in the vicinity of the surface of the semiconductor substrate.
2. Description of Prior Art
In the manufacture of integrated circuits, as well known, impurity ions are injected or diffused into the main surface of a semiconductor substrate, and then various film structures are formed thereon. To determine whether this process has been accurately carried out, it is necessary to inspect the electronic state of the surface of the semiconductor substrate.
One inspection technique, an electromagnetic and non-contact evaluation technique, is disclosed in JP, A, 22034/1986. In this technique, electron-hole pairs are generated by light emission to the semiconductor substrate. The electrons and holes, thus generated, are excess carriers, and are recombined by recombination centers distributed on the surface of the substrate, and after a lapse of a period of time longer than the lifetime of the carriers, reach a stationary state which is caused by the difference between a quantity of the carriers generated by light excitation and that lost by recombination. In the above-mentioned technique, the substrate having reached the stationary state is irradiated with microwave. Even if the light irradiation is not conducted, the carriers in a thermal equilibrium state respond to the microwave to cause absorption thereof and emission of secondary electromagnetic waves (hereinafter these phenomena are generally called "absorption"), but if light irradiation is conducted, excess carriers generated thereby also cause absorption of microwave so that a quantitative response of the substrate to the microwave occurs. In other words, the variable amount of microwave absorption by the substrate reaches a value corresponding to the total number of excess carriers existing at the current point. In the above conventional technique, therefore, a measurement is conducted with reference to the variable amount of reflection which is complementary to the variable amount of microwave absorption. The rate of re-combination of excess carriers or concentration of the re-combination centers is indirectly measured to determine the amount of ion dose on the surface of the substate. This inspection method is generally called "microwave reflection method (in stationary state)".
In the above inspection method, the surface of the substrate is successively scanned while moving the substrate relative to the measuring apparatus, such as a microwave generator, microwave detector etc., in order to inspect the electronic state of the surface of the substrate at various points of the surface. During movement of the substrate relative to the measuring apparatus, the distance between the measuring apparatus and the surface of the substrate is varied minutely, thereby causing variation of the measuring conditions such as microwave output impedance from the side of the microwave generator and the like. The principle of the above measurement is based on an assumption that the surface of the substrate is evenly extended. In practice, however, the substrate has at the ends thereof uneven parts, such as edges or orientation flats, etc., which cause deviation of the measurement results.
Thus, the measurement conditions are varied according to the relation of geometrical position between the measurement apparatus and the substrate to cause errors in the measurement data. It is desired to improve the accuracy of the inspection of the electronic state of the substrate surface by preventing the effect of measurement errors as mentioned above.